There is a desire in the industry for higher circuit density in microelectronic devices which are made using lithographic techniques. One method of achieving higher circuit density is to improve the resolution of the lithographic patterns made in the photoresist film.
Radiation backscattering during exposure caused by reflections from the topographical features of the substrate are a significant contribution to linewidth variation and resolution problems.
A prior art technique for improving the resolution of lithographic patterns in photoresist involves forming multilayered resists. A thick polymer layer is first coated on the substrate over the surface topography to provide a planar surface upon which a thin imaging resist layer is uniformly coated. After the imaging layer is imagewise exposed to radiation, it is used as a blanket exposure or etch mask to delineate the planarizing layer. The image is developed from the imaging layer through the planarizing layer to the substrate. Although, multilayered resists substantially solve the problems caused by radiation backscattering from the substrate, they require additional processing steps resulting in increased process complexity and cost.
Allen et al., U.S. Pat. No. 4,810,601, issued Mar. 7, 1989, discloses a method of avoiding image distortion resulting from backscattering by adjusting the energy and length of exposure of an electron beam source to confine the beam to the top portion of the photoresist.
While such a process is suitable in those limited situations which are appropriate for electron beam exposure, there still is a need in the art for a method for avoiding image distortion resulting from backscattering for use with other types of radiation exposures such as ultraviolet/visible electromagnetic radiation exposure.
It is therefore an object of the present invention to provide a novel method for imaging of a photoresist.
Other objects and advantages will become apparent from the following disclosure.